The present invention relates to electromagnetic clutches and more specifically relates to control circuits for such clutches.
Among other uses, electromagnetic clutches are applied to engage a drive line in a harvesting machine, in particular in a self-propelled forage harvester. Forage harvesters are often provided with a metal detector that generates a magnetic field through which the harvested crop flows. These metal detectors are incorporated in the electric circuit of the electromagnetic clutch and when metal is detected a signal is sent to disengage the electromagnetic clutch. However, the induction voltage resulting from operation of the metal detector can result in additional voltage being applied to the clutch which must be dissipated before the clutch will disengagement. This delay in the disengagement of the electromagnetic clutch is undesirable because the drive will continue to operate and possibly ingest the detected metal into the feed rolls of the harvester and possibly cause damage before the drive to the feed rolls is interrupted.